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    <p>
      The <em>IfcDateTimeResource</em> schema defines several
      generic date and time specific concepts that can be used to
      identify context within calendars, schedules, and time
      series. These concepts include:
    </p>
    <ul>
      <li>
        <em>IfcDate</em>, <em>IfcTime</em>, <em>IfcDateTime</em>
        and <em>IfcDuration</em>. All given values should be provided 
        in context and converted into a Gregorian date context and be 
        shall be processable by a receiving application.
      </li>
      <li>Time series, which are a set of discrete data each
      with an associated date and time stamp, allowing a natural
      association of data collected over intervals of time. Time
      series data can be represented using the following entities:
        <ul>
          <li>
            <em>IfcRegularTimeSeries</em>: Time series data arrive
            predictably at predefined intervals and are represented
            by the entity, and
          </li>
          <li>
            <em>IfcIrregularTimeSeries</em>: some or all time
            stamps do not follow a repetitive pattern and
            unpredictable bursts of data may arrive at unspecified
            points in time.
          </li>
        </ul><br>Time series data must be normalized using the
        following rules:
        <ul>
          <li>All time (universal, local, daylight savings, and
          solar) is normalized against the ISO 8601 standard
          GMT/UTC (Universal Coordinated Time).
          </li>
          <li>The normalized data refer to the preceding time unit.
          </li>
          <li>Any rollover is handled by the application providing
          the data. Rollover occurs, for example, when the
          measurement device resets itself while measuring and the
          recording data do not include the data measured before
          the reset.
          </li>
          <li>Only the time when data are taken is recorded.<br>
          </li>
        </ul>
      </li>
      <li>Time associated with processes such as resource
      allocation (<em>IfcResourceTime</em>), time for task
      completion (<em>IfcTaskTime</em>), work patterns
      (<em>IfcWorkTime</em>), and scheduled events
      (<em>IfcEventTime</em>).
      </li>
    </ul>
    <blockquote class="note">
      NOTE&nbsp; The schema <em>IfcDateTimeResource</em> includes definitions
      that are based on <a class="int-ref" href=
      "../../bibliography.htm#iso-8601">ISO 8601</a>
    </blockquote>
    <blockquote class="history">
      HISTORY&nbsp; This schema has been significantly modified in
      IFC4. The original concepts of <em>IfcDateTimeResource</em>
      and <em>IfcTimeSeriesResource</em> were introduced in IFC2.0
      and IFC2x2 and merged into the <em>IfcDateTimeResource</em>
      in IFC4.</blockquote>
    <blockquote class="change-ifc2x4">
      IFC4 CHANGE&nbsp; The new types <em>IfcDate</em>, <em>IfcTime</em>,
      <em>IfcDateTime</em> and <em>IfcDuration</em> cancel and
      replace the previous entities <em>IfcCalendarDate</em>,
      <em>IfcDateAndTime</em>, <em>IfcLocalTime</em>, and
      <em>IfcCoordinatedUniversalTimeOffset</em>.
    </blockquote>
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